Chain Dynamics and Glass Transition of Dry Native Cellulose Solutions in Ionic Liquids
Dry native cellulose solutions in 1-butyl-3-methylimidazolium methylphosphonate (EMImMPO3H), 1-butyl-3-methylimidazolium acetate (EMImAc), and 1-butyl-3-methylimidazolium chloride (BMImCl) ionic liquids (IL) were investigated using subambient linear viscoelastic oscillatory shear. Glass transition temperatures (Tg) of solutions with various cellulose concentrations up to 8.0 wt.% were observed as the peaks of loss tangent and loss modulus 𝐺" in descending temperature sweeps at 1 rad/s. Cellulose/IL solutions showed a minimum in Tg at ~2.0 wt.% cellulose content before increasing with cellulose concentration, suggesting a perturbation of the strongly structured IL solvents by the cellulose chains. Isothermal frequency sweeps in the vicinity of Tg were used to construct time-temperature-superposition master curves. The angular frequency shift factor as a function of temperature indicates Arrhenius behavior within a 9 K range near Tg, allowing calculation of fragility, which was found to be constant up to 8.0 wt.% cellulose concentration. This result implied that increasing cellulose concentration initially decreases Tg due to disrupted ionic regularity of ILs, but does not seem to change their fragility.
|Chain Dynamics and Glass Transition of Dry Native Cellulose Solutions in Ionic Liquids
|Public Domain Mark 1.0
|Publisher Identifier (DOI)
|February 25, 2021
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